Solid-state lighting arrays are used for a number of lighting applications. For example, solid-state lighting panels including arrays of solid-state light emitting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A solid-state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs), which may include inorganic LEDs, which may include semiconductor layers forming p-n junctions and/or organic LEDs (OLEDs), which may include organic light emission layers. Typically, a solid-state light emitting device generates light through the recombination of electronic carriers, i.e. electrons and holes, in a light emitting layer or region. A solid-state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs).
Cree, Inc. produces a variety of recessed downlights, such as the LR-6 and CR-6, which use LEDs for illumination, as well as a variety of LED bulbs intended to replace standard incandescent bulbs. Solid-state lighting panels are also commonly used as backlights for small liquid crystal display (LCD) screens, such as LCD display screens used in portable electronic devices, and for larger displays, such as LCD television displays.
Solid state lighting devices are typically powered with a DC signal. However, power is conventionally delivered in AC form. It is therefore generally desirable for a solid state light fixture to include an AC to DC converter to convert AC line voltage to a DC voltage.
Boost converters can be used to generate DC voltage from an AC line voltage with high power factor and low total harmonic distortion. The voltage of an LED-based load may be higher than the peak of the input (line) AC voltage. In that case, a single-stage boost converter can be employed as the driver, achieving high power efficiency and low cost. For example, a power factor corrected (PFC) boost converter which converts 120V AC, 60 Hz, to 200-250V DC output could be used to drive an array of high-voltage (HV) LEDs at a power level of 10-15 W.
In some cases, however, the voltage of an LED-based load may be lower than the peak of the input voltage waveform. In that case, it may be desirable to use a buck-boost converter that is capable of supplying an output DC voltage that is either higher or lower than the input voltage.